The Unexpected Revelation: Transforming Seedlings into Super Plants With a Whiff of an Unconventional Chemical

The practice of 'priming' plants involves exposing them to certain chemicals during their seed stage, with this exposure influencing growth patterns later on.

Scientists have observed that seeds treated with ethylene gas undergo an increase in growth and stress tolerance. This discovery, which involves enhanced photosynthesis and carbohydrate production in plants, may act as a critical breakthrough in enhancing crop yield and fortifying them against environmental stressors.

Plants are not exempt from stress, often triggered by heat and drought. Under such conditions, plants may not hit their growth potential or be as productive, posing challenges for farmers. A popular solution among scientists is to genetically modify these plants to make them more resilient.

However, plants that are genetically modified for greater crop yield usually display lower stress tolerance since they prioritize growth over stress protection. Conversely, plants modified to survive stress conditions commonly produce less as they prioritize protection over growth. This challenge adds to the difficulties in enhancing crop production.

My research endeavors revolve around how the plant hormone ethylene regulates growth and handles stress responses in plants. Publish in July 2023, a study by my lab made a critical observation; when seeds germinate in darkness – as they usually do underground – the addition of ethylene boosts both their growth and stress tolerance.

Unlike mobile organisms, plants cannot escape stressful environmental conditions such as heat and drought. Their growth, development, and stress-handling mechanisms are shaped by a variety of environmental signals like light and temperature. Plants produce diverse hormones that form a regulatory network, helping them adapt to changing conditions.

Ethylene, a gaseous plant hormone, was discovered a century ago. Subsequent research revealed that all land plants studied produce ethylene, which controls growth, stress responses, and other processes, including leaf color changes in autumn and fruit ripening.

My lab specializes in understanding how plants and bacteria sense ethylene and how it collaborates with other hormone pathways to regulate plant development. During this research, my group stumbled upon an unexpected discovery.

We conducted an experiment where seeds germinated in darkness were exposed to ethylene gas over a few days. After removing the gas, we relocated the seedlings to light, intending to make the plants mature and collect their seeds for future experiments.

A few days later, we observed that the seedlings exposed to ethylene were significantly larger, boasting bigger leaves and more complex and longer root systems. The plants also grew faster throughout their entire lifecycle.

I collaborated with my colleagues to explore if various plant species exhibited growth stimulation when exposed to ethylene during seed germination. Irrespective of whether the seeds were of tomato, cucumber, wheat, or arugula – all seeds that were subjected to short-term ethylene treatment grew bigger.

What made this observation intriguing was the fact that short-term ethylene exposure also enhanced tolerance to stresses like salt exposure, high temperature, and low oxygen conditions. This phenomenon is often termed as priming effects, a term analogous to priming a pump for more effortless and quicker start.

My lab has been working relentlessly to identify mechanisms enabling ethylene-exposed plants to grow larger and handle more stress since this experiment. We have come across a few potential reasons.

One is that ethylene priming increases photosynthesis, the process plants use to make sugars from light. Part of photosynthesis includes what is called carbon fixation, where plants take CO₂ from the atmosphere and use the CO₂ molecules as the building blocks to make the sugars.

During photosynthesis and carbon fixation, plants take in sunlight and convert it into the sugars that they use to grow.

My lab group showed that there is a large increase in carbon fixation – which means the plants are taking in much more CO₂ from the atmosphere.

Correlating with the increase in photosynthesis is a large increase in carbohydrate levels throughout the plant. This includes large increases in starch, which is the energy storage molecule in plants, and two sugars, sucrose and glucose, that provide quick energy for the plants.

More of these molecules in the plant has been linked to both increased growth and a better ability for plants to withstand stressful conditions.

Our study shows that environmental conditions during germination can have profound and long-lasting effects on plants that could increase both their size and their stress tolerance at the same time. Understanding the mechanisms for this is more important than ever and could help improve crop production to feed the world’s population.

Written by Brad Binder, Professor of Biochemistry & Cellular and Molecular Biology, University of Tennessee.

Adapted from an article originally published in The Conversation.